Amy is trapped for decades in an alternate timeline, forcing Rory to choose between two versions of his wife.

Taking a break from their recent troubles, the Doctor (Matt Smith) brings his companions Amy Pond (Karen Gillan) and Rory Williams (Arthur Darvill) to Apalapucia, the second most popular vacation planet in the universe. But instead of the paradise that was promised, the Doctor and his friends find themselves in a sterile hospital-like environment. While Amy goes back to the TARDIS to retrieve her cell phone, the Doctor and Rory enter a room by pressing a green button. When Amy follows, she presses the red button to open the door and enters the same room only to find that she is alone.

In the other version of the room, the Doctor and Rory find a mirror that allows them to see and hear Amy. To their astonishment, Amy tells them that she has been waiting for them for a week. The Doctor theorizes that Amy is in a faster timeline, but when Rory tries to follow Amy into the alternate timeline the door opens to yet another alternate timeline where Amy isn't present. Rory returns to the Doctor and they learn that Apalapucia is under medical quarantine for a disease that is fatal to Time Lords and the Apalapucians. The facility is manned by white robots with blank faces that administer drugs that would be fatal to humans.

The Doctor warns Amy to avoid the injections at all costs and to stay safe until they can find her. She writes a message on a wall for the Doctor and waits. On the TARDIS, the Doctor uses the mirror to lock in on Amy's current timeline. Because the virus would prove fatal to him and humans are immune to it, the Doctor sends Rory out to save Amy armed with his sonic screwdriver, the glass scope and a pair of glasses to communicate with the Doctor. Soon enough, Rory finds Amy and he is startled to find that she has waited 36 years for them to return. She is also extremely angry at the Doctor and Rory for seemingly abandoning her to her fate.

Rory protests and angrily remarks that the Doctor simply got to the timeline later than they should have arrived. The older Amy is a fierce warrior and intelligent enough to build her own sonic screwdriver. She also keeps an unarmed robot as a pet she calls "Rory." Older Amy also refuses to help the Doctor and Rory save her younger self because it will negate her existence. After Rory yells at the Doctor for leading them into this danger, they accidentally make contact with the younger Amy in the past. Rory uses the mirror to let both Amys talk to each other. And although the older Amy initially refuses to help, she relents when the younger Amy reminds her of their mutual love of Rory.

Older Amy finally agrees to assist them if the Doctor will bring her onto the TARDIS as well. The Doctor ponders it and he says that it should be possible for both Amy's to exist on the TARDIS. Using a common memory of their first kiss with Rory as a shared thought across two points in time, the Amys are drawn together by Rory's manipulations of the facilities' timeline machines. Together, the two Amys and Rory fight their way back to the TARDIS. But the younger Amy is sedated by one of the robots and she falls unconscious. Rory carries her into the TARDIS to safety. But once they are inside, the Doctor looks older Amy in the eyes and locks her out of the TARDIS.

The Doctor explains to Rory that he lied earlier. Only one Amy can leave on the TARDIS. Rory refuses to abandon the older Amy, so the Doctor gives Rory the choice of which Amy to save. Older Amy and Rory reestablish their connection and he starts to unlock the door for her. But she stops him and pleads with him to keep the door shut and leave without her. When the medical robots come up behind her, older Amy allows herself to be taken at last as the TARDIS fades away. When the younger Amy wakes up, she asks about her alternate self. But neither the Doctor or Rory can bring themselves to tell her what they did.

Breakdown:

I suspect that this episode may have been constructed to be one of the least expensive stories of the season, with a heavy focus on the main cast and minimal guest performers. But if the writers had to make a low budget "Doctor Who" episode than this was the best way to do it. The Doctor's betrayal of the older Amy and her subsequent demise was haunting and powerful. The last scene where younger Amy questioned the absence of her older self ended on just the right note. But I still would have liked to have seen her learn what the Doctor and Rory had done.

Karen Gillan and Arthur Darvill usually get overshadowed by Matt Smith's performance as the Doctor, but this show clearly belonged to the Amys and their lone Rory. Well… their lone human Rory. The poorly drawn face on the robot Rory was really hilarious and it did slightly resemble Darvill's face. Gillan was also very striking as the angry and bitter older incarnation of Amy Pond. Her character is usually so non-threatening that it was almost a revelation to see Amy portrayed in such a different way. Older Amy also had an amusingly flirtatious side with Rory.

But what really made the episode great was the heartbreak of older Amy's final moments. This was her Raggedy Doctor who she loved all of her life. He was her protector, her friend… and he left her to die. Or worse, the Doctor left her to face nonexistence as he tried to dismiss her as not being real. But the older Amy was very real and Rory gets a lot of points for not willingly abandoning his older wife for the younger version of herself. And we saw him make his choice. He was going to save the older Amy because he couldn't stand to see her suffer. It was odd to hear the Doctor claim that two Amy's couldn't exist on the TARDIS because we had seen it earlier this year in the mini-episodes "Space" and "Time." However, from a dramatic stand point, it worked.

If anything, this episode reaffirmed the strong bond between Amy and Rory. Their marriage has some detractors in "Doctor Who" fandom, but it also gives them a different dynamic than any of the Doctor's previous companions. They're young and in love, and even an extra 36 years on his wife couldn't deter Rory's feelings for Amy. When both Amys finally came together, it led to some very warm and funny banter between Rory and his two wives. If both versions had managed to survive this episode, it would have been interesting to explore having the two Amy Ponds around for a while.

As much as I loved the darker ending we got here, it does bring up another important question: why are Amy and Rory still traveling with the Doctor? Rory's anger towards the Doctor was every bit as intense as the older Amy's was. The fate of Amy and Rory's daughter has already been settled and the sad truth is that if they travel with the Doctor for too long one or both of them will probably end up dead… permanently.

My guess is that they're sticking around for now in the hopes of finding a way to save the Doctor from the Impossible Astronaut. Anything beyond that is going to need a very compelling reason to get them to remain on board the TARDIS. And one last thing to keep in mind: we've already seen the future of Amy and Rory last season during the Silurian two parter. In the distance, we saw an older Amy and Rory waiving at their present day counterparts and we've yet to catch up to that point in time.